Oligonucleoside methylphosphonates have been used to study the function of specific RNA sequences in biochemical and intact cellular systems. See Miller et al, Biochemistry 20, 1874-1880 (1981) and Jayaraman et al, Proc. Nat'l Acad. Sci. 78, 1537-1541 (1981). Since these nonionic nucleic acid analogs can be taken up intact by mammalian cells and certain bacterial cells in culture, these compounds promise to be useful reagents for exploring and regulating the function of nucleic acids within living cells. See, in this regard, the above-mentioned U.S. applications Ser. No. 206,297 and Ser. No. 363,230.
While various procedures have previously been described for synthesizing oligonucleoside methylphosphonates and the like, there is a real need for a synthesis method which will efficiently and effectively provide oligomers of the desired sequence and length in the yields and amounts required for use.
The synthesis of the methylphosphonate analogs on a silica gel support has previously been described (Miller et al (1983) Nucleic Acids Res.). In that work, protected nucleoside 3'-methylphosphonic chlorides or tetrazolides were used as synthetic intermediates. While oligothymidine methylphosphonates could be efficiently synthesized by this procedure, low yields were encountered when other nucleosides, particularly d-[(MeO).sub.2 Tr]ibuG, were used. Recently the preparation of oligonucleoside methylphosphonates on a glass support using nucleoside 3'-methylphosphine chlorides as reactive intermediates has been described (Sinha et al, Tetrahedron Letters, 24, 877-880, 1983). However, there continues to be a need for an efficient and convenient method for synthesizing oligonucleoside methylphosphonates of a desired sequence.